Poly α-olefins comprise one class of hydrocarbon lubricants that has achieved importance in the lubricating oil market. These materials are typically produced by the polymerization of α-olefins typically ranging from 1-octene to 1-dodecene, with 1-decene being a preferred material. Polymers of lower olefins such as ethylene and propylene may also be used, including copolymers of ethylene with higher olefins, as described in U.S. Pat. No. 4,956,122 and the patents referred to therein. The poly α-olefin (PAO) products may be obtained with a wide range of viscosities varying from highly mobile fluids of about 2 cSt at 100° C. to higher molecular weight, viscous materials that have viscosities exceeding 100 cSt at 100° C. The PAOs may be produced by the polymerization of olefin feed in the presence of a catalyst such as AlCl3, BF3, or BF3 complexes. Processes for the production of PAO lubricants are disclosed, for example, in the following U.S. Pat. Nos. 3,382,291; 4,172,855; 3,742,082; 3,780,128; 3,149,178; and 4,956,122. The PAO lubricants are also discussed in Lubrication Fundamentals, J. G. Wills, Marcel Dekker Inc., (New York, 1980). Subsequent to the polymerization of the α-olefin, the lubricant range products are hydrogenated to reduce the residual unsaturation. In the course of the hydrogenation, the amount of unsaturation is generally reduced by greater than 90%.
PAOs having a viscosity of 4 cSt are typically made from 1-decene and have a Noack volatility of 13-16% and pour point of less than −60° C. Certain conventional PAOs having a viscosity of 5 cSt are typically made from 1-decene and have a Noack volatility of about 9% and a pour point of less than about −57° C. PAOs having a viscosity of 6 cSt are typically prepared from 1-decene or a blend of α-olefins and have a Noack volatility of about 7% and pour point of about −60° C. These PAOs may be used alone or in conjunction with another material that serves as a base stock. The fully formulated engine oil may include at least a portion of a co-base stock.
A major trend in passenger car engine oil usage is the extension of oil drain intervals. Because engine oil users do not regularly check engine oil level and top off with supplement oil when needed, a need exists for lubricants that exhibits low Noack volatility to control oil consumption. (See ASTM D5800 Standard Test Method for Evaporation Loss of Lubricating Oils by the Noack Method.)
There also exists a need for a fully formulated engine oil that has a lower viscosity increase and viscosity after use for a given period of time when compared to conventional engine oils to maximize engine oil useful life. There is also a need for fully formulated engine oils with exceptional low temperature performance.
PAOs are one family of lubricants that provide extremely good Noack performance and simultaneously provide excellent low temperature properties and thus are an ideal fluid for extended drain applications.
The properties of a particular grade of PAO are greatly dependent on the α-olefin used to make that product. In general, the higher the carbon number of the α-olefin, the lower the Noack volatility and the higher the pour point of the product.